First off, sorry if this is in the wrong spot or if it's a known bug, someone from the reddit sent me here. Anyways:

Currently if you steal someone's creature with Simic manipulator, then it proceeds to die, no matter where it goes (GY, command zone, library) if it returns to the battlefield it will return under your(manipulators controller) control.

Simic manipulator doesn't seem to need to stick around either. It also doesn't matter how the creature returns (cast, reanimate, etc.)